Tween HeadbangersScore HUGE Record Deal

7/13/2014 12:45 AM PDT BY TMZ STAFF

EXCLUSIVE

The pint-sized heavy metal musicians who became a huge hit at Coachella have just signed a spectacular contract with a huge record label that will make them the richest kids on their block.

The band -- Unlocking the Truth -- formed when the kids were just 10 and 11. They were so good they were quickly booked on Amateur Night at the Apollo. But they hit it big at the ripe old ages of 12 and 13 ... when in April they became the youngest group ever to perform on the main stage at Coachella.

The kids -- who are now 3 strong with a 13-year-old bassist -- got noticed by none other than Sony and just signed a great deal, which was filed with the court and obtained by TMZ. Under the contract, they'll get the following advances:

-- $60,000 for the first album-- $325,000 for the second-- $400,000 for the third-- $450K for the fourth-- $550K for the fifth

Mind you, if they sell enough records they'll also get royalties.

And get this ... their influences are Metallica, Slipknot and Disturbed.